UNIX VII: Compilers

• A compiler is a program which translates a program written in a high level language into assembly or machine language.

• Most UNIX computers come with a C compiler called cc, but unfortunately many of these compilers are nonstandard. In this class, we will be using the GNU C compiler.

• [The GNU project was started by Richard Stallman to develop quality free software for UNIX machines. GNU stands for GNU's Not Unix.]

• To access the GNU C compiler on Athena, first type add gnu. Then to compile the source code in the file test.c, type gcc test.c -g -ansi -o test.
  • The -g option tells the compiler to include debugging information in its output.
  • The -ansi option tells gcc to compile your code according to the ANSI specification of the C language.
  • The -o test tells gcc to put the executable output in a file named test.

• [For obscure historical reasons, if you don't add the -o test the default behaviour is to put the executable in a file named a.out.]

• To run your program, just type test. To run your program under gdb (the GNU debugger), type gdb test. Running your program under a debugger allows you to step through it one statement at a time and to examine the state of the computer's memory, among other things.